Abstract
An efficient synthesis of highly functionalized chiral β-amino ester derivatives containing benzothiophene and benzothiazole moieties is developed by a Mannich-type reaction using a cinchona alkaloid-derived thiourea catalyst. The desired products were obtained in good yields and high enantioselectivities (~86% yield, >99% ee) using to the optimized reaction conditions. The synthesized compounds were characterized by 1H-NMR, 13C-NMR, IR, and HREI-MS analyses. The bioassays identified that compound 5dr has excellent antifungal activity, with a 60.53% inhibition rate against F. oxysporum, higher than that of the commercial agricultural fungicide hymexazol, whose inhibition rate was 56.12%.
Highlights
Chiral β-amino acid ester derivatives exhibit diverse biological properties such as antitumor, immunostimulating, and antiphlogistic activities [1–4]
We report an extension of our previous study by using potentially bioactive benzothiophene and benzothiazole moieties [48–50] as the building blocks for the synthesis of chiral β-amino acid ester derivatives
The enantioselectivity of 5dc, 5hc, 5lc and 5pc was higher than the other compounds, probably because the malonate ester was a benzyl ester, and steric hindrance affected the Mannich-type reaction between the imines and benzyl esters
Summary
Chiral β-amino acid ester derivatives exhibit diverse biological properties such as antitumor, immunostimulating, and antiphlogistic activities [1–4]. They have been widely used as peptidomimetics and are found in many natural products. Β-Lactams, which exhibit a wide range of biological properties such as antibiotic, antiviral, and protease inhibitor activities. Β-Amino acid ester derivatives can be used as building blocks for the synthesis of these types of antibiotics, making them useful in drug synthesis and other fields [10–13]. The asymmetric synthesis of β-amino ester derivatives or β-lactams has received much attention in organic synthesis over the past few years [3,14]. In 2011, Bull and coworkers reported the first example of an intramolecular cyclization of the ester enolate imine for the preparation of monocyclic β-lactams (Figure 2) [15]
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